CHAPTER II. THE HYGIENE OF HABITATIONS. (Part 11)

always lu' rriiu'iiilx'fc*! that intiic oF tlu' ^mtihs arc killed hy cold tfiniu'ratiiirs and that the j)atli()- geiiic hactcria may )v as actixv as in warmer raw milk. Infected milk is thcrcloi-c a daniicntii^ milk to drink wJiile raw, even if kej)t in a eool state. Cold /.v oiih/ a nihnihlr aid in iiiilh pir.srrrdfio)!, uofhiucj tiiorr. Milk Preservation by Sterilization. —Sterilization is tlu' only method I»y which it is possible to make abso- lutely certain that milk contains neither i)acteria nor their spores. It is the only method of jireservation which rids milk of pathogenic bacteria. Sterilization is defined as the "heating of milk to the boiling-point of water and above for a time sufficient to destroy all organic life and all bacteria and their spores." Complete or ahsoJntc sterilization camiot be accom- plished unless the milk is heated well above the boiling- point — 220° to 240° F. — in autoclaves or sealed cham- bers under steam-pressure for a prolonged time, varying from one-half to two hours. This is the only means which assures complete destruction of all sj)ores and pathogenic spore-bearing bacteria, like those of tetanus, etc. Simple boiling is also sometimes called sterilization. While this kills most germs and even a few spore-bearing germs, it does not make certain that all spores have been killecl. The objections to sterilization of milk, complete as well as incomplete, by boiling, are that certain changes are produced in milk !)>■ the heat. The ell'ects of boil- ing and sterilization are as follows: 1. Change in color due to the browning or caramdi- zation of the lactose. 138 HYGIENE OF FOODS AND FOOD SUPPLY 2. Change in taste, the milk receiving a different cooked taste. 3. The destruction of all lactic acid bacteria, fer- ments, enzymes, as well as all other germs in the milk. 4. Coagulation of the albuminoid matter in the milk. The sum of these changes is that the milk is not only less tastj', but is much less digestible and fit for food. For infant-feeding it has been found not appropriate, and some observers claim that it may cause scurvy and rickets. Milk Pasteurization. — The word "pasteurization" has been so much used and missused that it is about time to discard it entirely, for it has no intrinsic meaning and simply confuses the minds of those who use it promiscuously. Pasteur's name is applied to a process which is carried out in many and various ways, and not always with scientific accuracy. The official definition of the term is "the heating of milk to a degree of heat sufficient to kill all most active germs; in general, the word is applied to any kind of heating of milk short of boiling. It is obvious that until a definite attempt is made to define the degree of heating and the time of heating and the exact procedure, the term will embrace various meanings, according to the whim and methods of each commercial or other concern using it. As Rosenau says: ''We should protest against a word which means a generality." And as he further remarks, the two main dominant factors that control the temperature and time at which the milk should be pasteurized are (1) "the thermal death-points of pathogenic bacteria, and (2) the ferments in the milk." MIl.K PRESERVATmX 130 'I'lif aim ami jxii-posc of so-called |)a>t('iiri/at ion is (1) to kill all iiio^t actixc hactcria. especially |)atlio^eMi(', {-) to lea\c the " t'eniieiits" imalVected, and {'.]) t(3 ehaiifie the milk as little as possii)|e in its general appearaiur, taste, and di^estil)ilit\ . There is as yet no unanimity of oj)ini()n as to the de<;rees and time at whicJi these conditions are reache(|. Accordiiifi to Rosenau a heating of milk for twenty minutes at a temperature of 140° F. al)solutely destroys the tubercle hacilli, tyjjlioid, di})litheria, dysentery, cholera, and other germs, hut not all the necessary and valuable ferments in the milk. \ot onl- the bacteria but their toxins, especially those of diphtheria and tetanus, are likewise destroyed at such a heatinj;. Tliere are, how- e\er. certain spore-bearing bacteria and bacterial toxins which remain unaflected at these temperatures. These spore-bearini: iierms are fortunately rare. Chemical Preservation. The difhcultx' of kee])ing milk sweet for a shorter or longer time after milking, led to the use of chemical preservatives, .\mong those formerly used are borax, boracic acid, salicylic acid, peroxide of hydrogen, and formalin. At present the use of any chemicals for milk preservation is strictly forbidden, although it is still more or less practised in secret. Borax and boracic acid were used in (piaiitities of ten grains to the (piart of milk. \Mien used either singly or in combination they may preserve the keei)ing quality of the milk f(»r twenty- four to forty-eight hours. Salicylic acid is a more powerful i)reservative. but its bitter taste makes it unfit for use exce|)t in very minute (piantities. l-'or- malin, which is a 4(1 j)er cent, solution of fornialdehyde. 140 HYGIEXE OF FOODS AXD FOOD SUPPLY is a powerful disinfectant. P^ven very small quanti- ties can greatly enhance the keeping qualities of milk. One part of formalin to 50,000 of milk, or about one teaspoonful to a forty-quart can of milk, will keep the milk sweet for from twenty-four to forty-eight hours. The objections to chemical preservation are the following: 1. The chemicals referred to are even in minute doses injurious to health. As they are injurious to adults, it is apparent that they must be even more harmful when ingested by delicate or sickly infants, for whose use most of the milk is intended. 2. They change somewhat the digestibility of the milk. This is notably the case with formalin, which hardens the proteid matter. 3. A continuous and steady use of those chemicals will result in gastro-intestinal disturbances and intoxi- cation, especially in children. 4. The use of chemicals, once permitted, even in minute doses, is bound to produce carelessness on the part of producers who will rely more upon the keeping qualities of the chemical than upon the cleanliness of production. 5. As soon as chemical preservation of clean and good milk is allowed, it will be impossible to prevent the use of chemicals in the case of bad, old, and partly spoiled milk, and this increases the danger of the use of milk. The use of harmless preservatives has also been urged. Among these are peroxide of hydrogen, oxygen, and carbon dioxide. Peroxide of hydrogen is used in the amount of about two ounces to the forty- MILK IXSI'I'XTIOX AM) TESTlXd Ml quart milk < ;iii. It destroys most of tlie bacteria and at tlie same time disapjjears itself in the form of free oxyjjeii. 'rite use of hydrojjen peroxide lias not been tried exteiisi-ely. The chemical is com|)arati\cly ex- j)eiisi-e and its \alue as a preserx ati'e is |)roi)lematic. Oxyjjen has been advocated as a disinfectant in milk; it is j)erfectly harmless and escapes after destroyiiifj the germs. Tlie exj)ense and tlie lack of proper ai)pa- ratus iiave so far made this process impracticable. ('arl)on dioxide is said to destroy most germs in the milk when n>cd under ])ressure of 7") ])ounds; the gas is harndess, does not change tlie character of the milk, and may be removed by aeration. This pro- cess is being ex])Ioited In a coTnin(>rcial concern, but its .scientific and practical value still remains to be demonstrated. MILK INSPECTION AND TESTING. Methods of Examination and Testing. The met hods of examining and testing milk for the difl'ercnt impuri- ties it may contain, and detecting the adulterations to which it is often subjected, are i)hysical, chemical, and i)aeteriological. I'hi/.siatl K.rdiiiliiiition. — By the i)hysical examina- tion are determined the appearance, color, odor, and specific gravity of the milk, together with the \aria- tions frotn the normal. f'hrinicdl E.ntiiiituitidii. This determines the exact amount of solids in the milk, also tlu* exact percentage of each solid in the fluid. 142 HYGIENE OF FOODS AND FOOD SUPPLY Bdcteriologlcal Examination. — This determines the number of bacteria in the milk and the presence or absence of pathogenic bacteria. Precautions. — The jjrecautions to be taken in the examination of milk are: (1) That the milk is thor- oughly mixed; (2) that it is not partly frozen; (3) that the milk to be tested has not been partly churned or partly separated from its cream; (4) that it is not partly or wholly coagulated. In order to make proper tests, fair samples of the milk must be taken from a given quantity of the marketed milk, and precautions must be observed in the manner of taking samples, so as to obtain a fair and just sample of the whole quantity instead of only a small part of the fluid. For this a thorough mixing of the milk is necessary in order to give it uniformity. Partly frozen milk will not give a good test, because the frozen part represents the watery part of the milk, and the rest of the milk will show a richer fluid and a higher percentage of solids. Milk which has been partly churned and has butter granules floating in it, or milk from which the cream has been wholly or partly separated, will naturally not give the normal percentage of fat in the fluid; thus the sample of the milk taken may not be a fair sample of the whole fluid. Milk which has been partly or wholly coagulated will not give a fair sample for testing because of the separation of the whey and solids. Before samples are taken milk which is partly frozen must be thawed, so that the whole fluid be- MILK l\srK(T/(>.\ AM) TKSl/.(; W'A conu's uniform; milk which has hccu partly cliiiriicd and contains hnttcr i:'''""iulcs fhtatini: in it must he heated, sn that the-e ^rainilcN melt; milk which has iteen i)artly or wholly coa^Milated mn>t he treated with alkalies sufficient to dissolve the coafiulum; milk which lias heen partly separated from its cream must he thoroughly mixed and made uniform. In mixini; milk care nmst l)e taken not to stir it too \ iolentlx-. so as to churn the milk or to mix it with air. The best means of mixinfj milk and of getting a uniform mixture is hy j)ourin^' it from one vessel to another. Physical Examination. — The physical examination of milk i> of -er- threat importance, and may gi\e valuable information to the inspector. The color of the milk, its opacity, its resistance to the immersion of a lactometer, its adherence to the instrument, the visibility of the instrument through the glass test- tube, are all valuable indications in the hands of an experienced inspector. Milk which is bluish in color, which allows the lactometer to sink with little resist- tance, which runs down the instriunent in thin bluish streaks, which hardly adheres to the instrument, and which is so little opaque that the instrument is readily seen through the test-tube, is a milk which is poor in solids and which is i)robably either skimmed or watered, or both skinmied and watered. Crvmii (i(tiu/r.- Milk is often testetl by the cream guage, pioxdpe. iind lactoscope. The cream gauge is simply a gra«luated glass test-tube in which the milk to be tested is allowed to .stand for twenty-four hour>. .\t the end of this time the amount of the cream. a~< indicated in the yellowish layer on to]), i-- 144 HYGIENE OF FOODS AND FOOD SUPPLY read off. A good milk usually shows about 14 per cent, of cream. In order to facilitate the better separa- tion of the cream, the milk is mixed with an equal amount of water and the resulting layer of cream is multiplied by 2 to show the actual amount of cream in the milk. The milk in the gauge should be put in a cold place, which favors the separation of the cream. This is a test upon which not much reliance can be placed. Pioscoye. — The pioscope (Heeren) is a small in- genious instrument to test the quality of milk by its opacity and color. The instrument consists of a small rubber disk with a small depression in its center, and of a glass plate painted in segments of 'arying shades of color, representing the color of cream, rich milk, normal milk, poor milk, skim milk, watered milk, etc. The inspector takes a drop of the milk to be tested and places it in the central depression of the hard-rubber disk, covers it with the glass plate, and compares the opacity and color of the milk with the various segments in the circle. In the hands of an experienced inspector this is a fairly trustworthy test. Lactoscope. — The lactoscope (Feser) also tests the milk by opacity. The instrument consists of a grad- uated glass cylinder, in the center of which, at the bottom, is fixed a small white rod with several black lines on its face; 4 c.c. of the milk to be tested are put into the cylinder, making the black lines on the rod invisible through the opacity of the milk. The test consists in carefully measuring the amount of water needed in the cylinder to render the fluid trans- parent, and to make the black lines upon the rod Mii.K i\si'i:(r/(i.\ ..\i> Ti:sri(i 11.") visihlc. It is ohvioMs that the poorer tlie (iiiality of tlu' milk tlu' less water will it he necessary to add to the c.Nhiider in order t»» make the mixture transparent; and, on the eontrary. it will he necessary to arid more water the rieiier the milk. The instrument is jxrad- uated and shows the amount of estimated fat in the milk according to the lunnher of the cuhic centimeters of water added. Specific Gravity. — The testing of milk hy its sj)ecific gravity is the test most frequently employed, and is very valuable in conjunction with the general physical examination of the milk. The specific graxity of milk depends on the solids in the fluid. Of these solids, sugar and the ])roteids are heavier than water, while the fat is lighter. The specific gravity of average normal milk is 1.029, and may vary in normal milk between 1.029 tf) 1.0.j2. The specific gra\ity is calculated at ()0° F. Milk which has been skimmed. /. r., from which a l)art or the whole of the cream has been separated, will show an increased specific gravity, because the absence of the fatty portion will make it denser and heavier. .V milk which is diluted with water will show a decreased specific gravity because it is made thereby much less dense and thirmer. Qiirmi/ir I.(trti)iiirfrr. The testing of milk with the Quevenne lactometer is based upon the relative s|)ecific gravity of the milk. Thi> lactometer is grad- uated from ].") to to. the scale reading as in ordinary hygromet«'rs and showing the corresponding degree of specific gravity. A good milk (at ••0'' K.i will read 32 upon this lactometer, showing a specific gravity lu 146 HYGIENE OF FOODS AND FOOD SUPPLY of 1.032, and average standard milk will read 29. A watered milk will read less than 29, according to the amount of water (0 being water), w^hile a skimmed milk will read more than 32 up to 40, according to the amount of cream subtracted. Lactometer of the Health Departvient of New York. — This instrument, extensively used in many places in the United States, is a larger instrument and is graduated differently from the Quevenne lactometer. According to this instrument it is assumed that 1.029 is the lowest permissible specific gravity for standard milk. The 29 degrees are divided into 100 subdivi- sions from the top figure 0 (showing the reading of water at 60° F.) to 1,00, which corresponds to 29 on the Quevenne instrument, or to the specific gravity of 1.029 on the ordinary hygrometer. The lactometer is graduated from 1 to 120. According to the Board of Health lactometer a poor market milk will read 100; a good rich milk will read between 100 and 110; a^skimmed milk will read between 110 and 120; while a watered milk will read under 100, the amount of water added being indicated by the reading, ?'. e., 10 per cent, of water has been added if the lactometer reads 90°, 25 per cent, if 75°, etc. This instrument is the most convenient for use, as the stem is longer and the degrees may be read more readily, and also the exact amount of the probable addition of water may be more readily calculated. As the lactometric readings are calculated at 60° F., corrections must be made for any difference in the temperature of the milk above or below 60° F. When the difference in the temperature is very great it MILK L\S1'1':(T1<L\ AM) TKSTIXd 117 is best to reduce or increase its temperature to within 10° of r)()°. The correction for the tenii)erature is the 0.1 (lcj,M*ee of tlie Quevenne lactometer for every (Icuri'c of temperature, and O.^i degree of the Board of Health lactometer for e\ery degree of temperature above or In-low 00°; added to the reading when the temperature of the milk is ai)ove 60° F., and sub- tracted from the reading when the temperature of the milk is below ()0° F. The usual rough correction for the Board of Health lactometer is 4° on the lac- tometer for every 10° on the thermometer, added or subtracted, according as it is above or below 00° F. As the specific gravity of milk is increased by skim- ming and decreased by watering, some milk dealers first subtract a certain amount of cream, thus in- creasing the specific gravity and lactometer reading, and then adrl sufficient water again to decrease the specific gra\ ity and lactometer reading to about normal, so as to deceive the inspector and give an adulterated milk a normal reading on the instru- ments. The only recourse of the inspector is