CHAPTER II. THE HYGIENE OF HABITATIONS. (Part 9)

a \ ci-y fa\oi'al)lc medium and are ca])al>le ot dex ('loi)in^- and increasing' in \cry lar^^e miinluTs. The most fre(|ueiit wa\ in which the ^M-rms of tiiese diseases i^ain access to the milk is thi-(Mi<i;h water, 'i'he diseharfjes of iiitV('t"d jjatieiits are often de|)osited upon the e])osed fifotind, or in shallow privy \anlts. ce>spools, etc.. ffom which they are wa>hed oil", seep throtmh the ^ronnd, and iiain access to tlie rivers, lakes, ponds, or wells, which serve as sources of water supply on farms. The txplioid hacilhis has l)een d"mon>trated in milk, and its vitality is so great that it retains its life for loiii,' periods. Hess reports findintr typhoid p-rms in >terili/.e(l milk after four months' time. Accordini: to Whipple ((|uote(l l)y Ward), "it has been estimated that in the Inited States at the i)resent time ahont 40 per cent, of the typhoid fever in cities is caused hy water; 25 per cent, hy milk."' Water infected with t.\phoid fever <,'erms ma- also he used as a washin<,' lliiid for milk nten^il^. or it may at times he used as an adulterant. Milk and Tuberculosis. TMl>crcnlo>i> may he trans- mitted thron^di milk heeau.se the tuherde hacilli which are the cause of the disease may he and are often found in milk. lle» fouml that 1(1 |)er cent, of the New ^ ork ( ity milk -upply contained tuhercle ''^I'i'li. and according,' to the investigation of others the |)resenee of the germs causing tnherc-ulosis has l)een clearlx tleinon-lrated so as to he heyond dispute. IIG HYGIENE OF FOODS AND FOOD SUPPLY Where do the tubercle germs which are found in milk come from? There is no doubt that some of these germs may come from accidental contamination from the outside. It is easy to see how persons who are afflicted with the disease may, while handling the milk, infect it with tubercle bacilli by coughing, spitting, sneezing; or the germs may be found in the dried dust floating around dairies, or on the hands and clothes, etc., of the persons handling the milk. There are also strong reasons for believing that a large or a considerable number of the tubercle germs found in milk are derived from the cow herself. Un- questionably a very large percentage of milch cows suffer from tuberculosis. According to many observers the average percentage reaches at least 25 per cent. This means that one cow in every four is affected. The disease is scattered over the entire country and there is hardly a herd that is completely free from its ravages. The question whether a tuberculous cow gives milk containing tubercle germs has been decided affirma- tively, at least insofar as it is now definitely known that cows suffering from advanced tuberculosis which involves the udder yield tuberculous milk. COWS' MILK. Definition. — ]\Iilk is the lacteal secretion obtained by the complete milking of one or more healthy cows. Composition. — Milk consists of water in which cer- tain solids are disolved or suspended. The relative proportion of the solids to the water varies from COWS' MILK 117 1 1 to 14 per cent., to S(l to Nil jut <riit.. with ;iii a\ cpii^re comi)()sition of i:> jut t-ent. solids .iiul n7 pci- cent. water. Solids. Tlu' //////,• soluls consist of siij^ar. fat, proteids, and minerals. Milk also contains a certain anionnt of ferment, j^as, and bacteria. MiUc-siKjdr (Lac'to.se). — Lacto.se is a sn^^ar pecniiar to milk, fomid in milk only, and dilferin^' somewhat from sugrose, dextro.se, and other sugars, ^^ilk-su^'ar is less sweet, less soluble, less subject to acid fer- mentation, has a specific gravity of 1..").). is solul)le in () parts of cold ami 2..') parts of boiling water; imder- goes lactic acid fermentation readily, but alcijliolic witli difficulty (Blyth). The average percentage of milk-sugar in milk is about "). var\ing but slightly from this. J///A'-/a/.— Milk-fat consists of the glycerides of various fatty acids, volatile and non--olatile. It is found in the milk in the form of an emulsion consist- ing of very numerous minute fatty globules held in suspension in the whole milk. The milk-fat is the most variable part of the milk con.stituents. Its proportion varies between 1 and ('» per cent., with an average of 4 per cent. Proff'ids- (itid AlhinninoifLs-. — The proteid matters "n milk consi.st of about SO per cent, of casein and I'd per cent, of other albumins, such as lacto-albnmins, protein, miclein. etc. The casein i^ the prin(i|)al and most \alnable j)ro- teid matter. Casein is coagulated by acids, by gastric juice, by rennet, and by a variety of (»ther substances; it is not j)recipitated or coagulated by heat which does 11<S HYGIENE OF FOODS AND FOOD SUPPLY coagulate the lacto-albumins. The projiortion of pro- teid matter in milk is less variable than that of fat. Its average is 3.25 per cent. Mineral Matter. — Milk contains various minerals in minute quantities. Milk-ash shows the presence of potash, soda, lime, magnesia, chlorine, iron, certain acids, etc. The percentage of mineral matter in milk averages 0.75. Composition of Average Milk. Water ... 87 per cent. Solids ... 13 per cent. Sugar . . . 5.00 per cent. Fat .... 4.00 per cent. Proteid . . . 3.25 per cent. Mineral . . 0.75 per cent. 13.00 per cent. Ferments and Gases in Milk. — Milk contains a number of ferments or enzymes (diatose, galactose, etc.) which are peculiar to every species of animals and have some function in the digestion and nutritive qualities of the milk. Milk when fresh also contains some gases, such as oxygen and carbon dioxide, due to the air it contains. Later the pressure of carbon dioxide may be due to fermentation. Appearance, Color, and Reaction. — Normal milk has a white or slightly yellowish color; it is opaque, has a a pleasant characteristic odor, and a sweetish taste. The reaction of milk is "amphoteric," /. e., slightly acid to litmus and alkaline to turmeric. The reaction becomes more acid with the advance of lactic acid fermentation; when milk becomes decomposed it develops ammonia and becomes alkaline in reaction. COWS' MILK 110 Specific Gravity. The \riij;lii .ind density of milk are j,n'('iit('r tliiiii of water, iiiasiiiiich as most of the milk solids aic of a relatively greater wei^dit and density than water. The heaxier and denser solids are the milk-sii<far, tlie })r()teid matter, and tlie mineral matter. Milk- sugar, specific gravity 1.55, proteids 1.20 (Rnhner). The only ingredient of milk which is lighter and less ilense than water is the milk-fat (0.92). If a liter of water at dO' F. (15° () weighs 1000 grams, a liter of milk at th(> same tem]:)eratnre will weigh from 102S to 10." !2. The specific gravity of average milk is usually 1.02!>, with x'ariations from 1.02S to i.o;;2. Milk without fat (skim milk) will have a much greater specific gravity, for the lighter j)art is with- drawn. The specific gravity of skim milk ranges from 1 .o;>5 to 1.010, according to the more or less thorough removal of the fat. The sj)ecific gravity of milk is increased hy low temperatni'e, hy the addition of solids, and hy the suh^traetion of fat. It is decreased i)y high tem- j)erature, hy the addition of water, and hy the addition of fat. Variations. Not only the (piantity hut also the (piality and the relati'e amr)uiits of the xarious milk ingredients vary greatly. Some of the factors on which the variation deix-nds are the hreed of the cow, age, kind, health, condition, care, food, drink, housing, treatment, climate, time of year, time of day, period of lactation. sea->oii, weather, and many others too numerous to mention. Most of the \aria- 120 HYGIENE OF FOODS AND FOOD SUPPLY tions produced by these factors are normal and are expressed in the relative quantity of milk produced, or the relative proportion of its various ingredients. Among the most important variations in milk are those which are found in colostrum, fore-milk, and the strippings. Colostrum. — For a certain period before and for several days after parturition the milk secreted by the cow differs materially in composition from nor- mal milk. While most cows "dry up" or cease to give milk in the last months or weeks of pregnancy there are some which continue to produce milk until the last days of pregnancy. During the ten days or two weeks before calving and from three to five or six days after the milk derived from cows is called "colostrum," or commonly "bee stings." Colostrum differs in composition from normal milk in that it contains a relatively smaller percentage of water (about 75 per cent.), relatively less milk-sugar and milk-fat, and relatively more protein matter, not in the form of casein but of lacto-albumin. To the latter it owes its property of coagulation l)y slight heat, a distinctive characteristic of colostrum. Colos- trum also contains a considerable number of blood corpuscles and of the so-called "colostrum corpuscles." The color of colostrum is distinctly yellowish and reddish, the taste peculiarly sweetish, and the odor specific. The ingestion of colostrum, especially when heated, is relished by a number of persons, although it has been known to cause gastric disturbances. The mixing of colostrum with the rest of the milk, or its sale, is forbidden by most municipalities. rows' MILK '2] Fore-milk and Strippings. -Tlicre is a (((usiderahlo (litlVrt'iicc ill the n-latixc ainoimt of iiiilk-t"at in tlic few streams of milk derixtMl at the l)e<;iiuiiii^' of milkiii<; from that of the few streams of milk <lcri\c(I at the end of the milkini:. The first milk, called fore-milk, contains sometimes less tJian 1 jxt cent, of fat, wliile the last, called stri|)pings, contains sometimes over .') per cent. Abnormal Milk. — Milk is sometimes abnormal in color, comijosition, etc.. and the sale of sncli milk is nsnally fori)id(len. Milk may l)e abnormal in color, distinctly red, bine, yellow, violet, etc. These abnormal colors of the milk are due to contamination with specific bacteria, wliich jirodnce the changes in color. The odor and taste of milk may also be abnormal. Thus milk sometimes is distinctly bitter or has the taste of garlic, onions, turnips, cabbage, etc.; it may bear some of the characteristic odors of strong vege- tables, etc. Milk may also have a distinctly fermenta- tive and "swilly" taste. Mo.st of these deviations from the normal are due to the food ingested by the cow. The bitter taste may be due to bacterial action. Milk may be abnormal in its consistency and become "slimy," "ropy," and viscous. In this condition it will not churn, nor will the cream separate, but other- wi.se it does not seem to be very harmful. 'J'he conrli- tion is due to the acticm of certain bacteria. Hopy milk is said to l)e a favorite article of food in Norway and elsewliere. and may be artificially produced by innnersing the >trm of "buttrrwt.rt" in milk (Hlyth). 122 HYGIENE OF FOODS AND FOOD SUPPLY MILK PRODUCTS. A consideration of milk production and inspection is incomplete without reference to the most important products which are a part of the milk industry. The milk products are the following: Cream, skim milk, butter, buttermilk, cheese, whey, condensed and evap- orated milk, milk powders, koumiss, kefir, etc. Cream. — Cream is the fatty portion of milk. It has the same composition as milk except that the percent- age of fat is very much larger. The percentage of cream in milk may vary from 6 to 50 or 60, and de- pends upon the process of obtaining it from the milk. The average amount of butter-fat in cream is 20 per cent.; the United States standard is 18 per cent. Production of Cream. — Cream is found in milk, in suspension, in minute globules of varying size. It is separated from milk by two processes: the gravity method and by aid of the centrifuge. Separation by aid of gravity is the oldest known process of gaining cream. It is based upon the fact that the suspended fat globules are of a lesser specific gravity than milk and rise to the surface when the whole fluid is left at rest. The common method is to pour the newly drawn milk into vessels and let them stand for a period of twenty-four to thirty-six hours. The cream rises to the surface and appears as a yel- lowish layer, and may be accordingly removed from the milk. Gravity methods may be divided into two, the shallow-pan and the deep-vessel setting systems. Cream is also separated by centrifugal force in MILK I'h'onrcTs 123 Sjx'cijil "scpiirators." wliidi iciikivc all I';i1 cxct'i)! O.I per cciif., which is left in llic ^kiiii milk. This is ;iii ('(lccti\c |>ro<'('ss of s('p;ii;it ion. Skim Milk. Skim milk i> milk Irom which ;ill or part of the cream has hccii rciiioxcd. The aiiioiiiit (if fat rcmaiiiiiii,^ in skim milk depends upon tlie mcthoils of x'paratiou and the thorou^hiies.s hy which it is done; it ma' \ary from less than 0.1 |>cr cent. to more than I per cent. Skim milk has a wiiite and somewhat l)hiish color, a hi<,di specific j^ravity \aryini; from l.O.'l.") to 1. 010. Because of the proteid tiiid ca.seiii it conlains, skim milk is a lii.udily nutritious and 'alual)lc food. 'I'lie sale of skim milk is pi-ohihited in nian> citie-^, not because of any harm that it may do, i)ut mainly on account of the ease witli which it is sul)stitutc(l for a whole milk and the (hHicnIty of detecting the adulteration. 'I'he casein ma>' he sep- arated froui the >kini milk and n-^cij foi' commercial purpo.ses, or it is used for the extraction of its milk- sujjar. Certain forms of cheese are larj^^ely made of skim milk. Blended Milk.- This term is applic(| to a modified milk in which one or more of the comi)onents of milk is increased or dimim'shed so as to furnish a modified milk with definite desired statecl percentafjes of certain of the milk comj)onents. It is larfjely used for infant foods, and mamifactureij according to formiike pre- scriiied liy physicians. Milk Products. The>e are ux-d chiefly a^ infant foods and are prejjared hy (omplete slow evajxiratiou of the water of the milk. .\s a rule the j)owders are mixed with some sugar and cereal products. 124 HYGIENE OF FOODS AND FOOD SUPPLY Condensed Milk. — Condensed milk is a milk from which a large part of the water has been extracted by slow evaporation. It is a very important article of commerce. Most of the condensed milk sold contains about 70 to 72 per cent, of water with 28 to .30 per cent, of milk solids, to which cane-sugar is added to increase the keeping qualities. Some thickeners may also be used to give the condensed milk more "body." The condensed milk is sterilized and sold in hermeti- cally sealed tin cans. When mixed with water it has a sweet, cooked taste. Butter. — Butter is the milk-fat of the milk gathered into a mass and separated from the milk or cream by the process of churning. Besides the milk-fat which it contains in the proportion of SO or more per cent., butter also contains water and minute quantities of the other ingredients of milk. Butter is commonly made of cream which is for this purpose ripened or made to undergo a process of lactic acid fermentation which is supposed to give the butter its valued "flavor." A "starter" made of buttermilk or sour cream is used to produce the "ripening." Butter is produced by churning or agitating the cream with paddles or spoons, in vessels, tubs, or barrels. These may be revolved by hand or machine power. The particles of fat adhere together and form distinct grains which are worked over, the buttermilk is removed b' several washings of water, and the whole turned into a mass by working and pressing together. The process of butter-making requires attention to temperature and other factors, upon which the flavor MILK J'U'oDrCTS 125 and (jiiiility nf the Itiittcr (Icpciid. Scirnr salt is ;uMc(l to tlir luittcr. Buttermilk. Hiittcniiilk i^ the residue left after butter is made fri)m milk or creaiu. It contaius all the iu^M-edieuts of milk exeej)t fat. It eoutaius millions of laetie aeid gcrm.s, and Ls a valuable food for man and animals. Cheese. — Cheese is "the solid and ripened product made by coasjulatintr the casein in the milk by means of acids or rennet." Cheese is made of whole milk which has undergone some lactic acid fermentation. It is tlien coagulated or rendered into two parts: one, an insoluble semi- solid composition consisting of the casein and fat, and the other of water (!)2 jut cent.), of nearly all the sugar, of the albumin and the mineral matter. The ins(tlul)le part is then j)resse(l out of the water and Worked ()('r by pressing and cutting, as well as by the addition of certain ferments, until the desired flavor and texture of the finished product is obtained. Cheese may l)e made of whole milk, of skim milk, and of milk to which cream has been added. The "rennet" which is added and used for the coagulation of the milk is an extract made from the fourth or digestive stomach of a young calf fed on milk. There are many \arieties and forms of cheese, depending upon the kinds of milk, temperature of fermentation, degree of aciditx', mamier of coagula- tion, kind of rennet. proce» of ripening, the specific "rii)ening" bacteria used. etc. The liquid j)ortion which is left after the in>oiul)le part has been removed in the process of cheese-making 126 HYGIENE OF FOODS AND FOOD SUPPLY is called whey. It consists mostly of water, but contains small quantities of albuminous matter and the sugar and most of the mineral matter of the milk. Whey is used for the extraction of milk-sugar, and is also a valuable food for domestic animals. The casein of the milk which is