lOlG] DAIRY FARMING DAIRYING. 71 



" It has been found that sterilization of pipettes is an unnecessary refinement 

 of technique and tliat a single pipette may be used for making preparations 

 from a long series of samples, provided it is carefully cleaned in glass-cleaning 

 solutions after each day's use and also cleaned by rinsing in fresh clean tap 

 water after using in each sample and before passing to the next sample. 

 Carelessness in cleaning pipettes causes marked errors in counts. 



" Growth of bacteria has been found to take place in the drops of milk as 

 they dry, so that it is important that these be prepared either from samples 

 containing preservatives or that the milk be dried quickly. No growth was 

 detected jn the dried films even after incubation in a moist, 37° C. incubator 

 for one to four days. The claim made by some that bacteria are removed 

 when the fat drops are dissolved by solvents does not seem to have any foun- 

 dation in fact. The dried milk solids-not-fat appear to act as a practically 

 perfect fixative, no detectable mechanical loss of bacteria taking place when 

 the fat drops are removed. On the other hand, serious errors in count are 

 introduced where the bacteria are stained in the milk before the dried films are 

 prepared, because in this way the bacteria are not always sufficiently stained 

 to make it posssible to detect the full number present. Where the fat drops 

 are left in the films, even though these be spread out so as to be in a very 

 thin layer, they tend to obscure bacteria and so lower the count. 



" The two essential conditions for making a reasonably accurate count of small 

 objects, like bacteria, under a microscope are that the objects themselves be 

 prepared in such a way that they are distinctly visible and recognizable and 

 at the same time evenly distributed over the field of the microscope. These 

 conditions are sometimes best secured in dried films, in other cases in liquid 

 preparations. Microscopical methods of examining dried milk films are of 

 value for two purposes: (1) They may be used for the rapid examination of 

 milk in order to grade it according to its bacterial quality, both the number 

 and the character of the bacteria present being taken into account. A micro- 

 scopical examination permits a fairly accurate guess as to the probable plate 

 count which will be secured from a given sample of milk. (2) They are also 

 useful as research methods, the microscopical method being the only known 

 method which permits a count of the number of individual bacteria. Micro- 

 scopical counts of the number of isolated individual bacteria and compact 

 clumps present in milk give figures which compare well with those obtained 

 where Petri plate methods of counting are used." 



Sources of bacteria in milk, M. J. Peucha {N. T. Produce Rev. and Amer. 

 Cream., Ifl {1916), No. 23, p. 925). — A popular discussion of the work previously 

 noted (E. S. R., 33, p. 876). 



Butter fat investigation. {Georgia Sfa. Rpt. 1913, p. 13). — In preliminary 

 work by F. H. Smith it has been found that cotton-seed oil may be detected in 

 the butter made from cows fed cotton-seed meal within 12 to 36 hours after 

 first feeding. From the time of the first appearance the test for cotton-seed oil 

 became more pronounced, until the seventh day, when the influence of the 

 oil appears to be at its maximum. After two, four, and six weeks continuous 

 feeding of oil the effect is no more pronounced, in most cases even less, than 

 at the end of the first week. When the oil is removed from the ration its effect 

 apparently disappears within one or two weeks. The results would indicate 

 that the oil is not transferred directly to the milk fat, but enters the milk fat 

 only after it has undergone some change in the animal body. 



The cheese value of milk of various compositions, E. Haglund {Meddel. 

 Centralanst. Forsoksv. Jordbruksomrddet, No. 116 {1915), pp. 29; K. Landtbr. 

 Akad. Handl. och Tidskr., 54 {1915), No. 7, pp. 583-609) .—Extensive experi- 

 43795°— No. 1—16 6 



