EXPERIMENTS OF AUTHORS 135 



the lactic acid group of organisms do not multiply as rapidly as 

 ordinary saprophytes, they reach a much higher maximum in the 

 end. It is to this family of bacteria that the second and maximum 

 rise is due. In time, also, the same inimical conditions begin to 

 act, and the lactic acid bacteria decline owing to the acidity and 

 to the lack of pabulum. Eventually, the medium, which twenty 

 days before was an ideal one for any organism, and mostly so for 

 those which came first, and which ten days before was favourable to 

 lactic acid organisms, is now favourable to no bacteria at all. 

 Accordingly, bacteria of all descriptions gradually die out, and the 

 medium is eventually left in possession of Oidium lactis and the 

 common moulds. That the destruction of large quantities of solid 

 albuminous substances may occur simply through bacterial agencies 

 has been conclusively shown in the so-called septic tank method 

 of sewage disposal. The death of bacteria under these circum- 

 stances always follows shortly after their enormous multiplication, 

 and how much is due to starvation or how much to poisoning 

 by the products of their own activity it is impossible to say. It 

 is, however, clear that the decomposition of large quantities of 

 albuminous substance is first accompanied by great bacterial repro- 

 duction, and this is invariably followed by a season of speedy and 

 extreme mortality of bacteria.^ In a general way that represents, 

 we believe, the changes taking place as represented in the record 

 we have considered. That there are two rises and two falls in the 

 number of bacteria, the first rise being due to extraneous organisms, 

 and the second rise to lactic acid organisms, we believe to be the 

 almost universal rule in untreated " natural " milk. 



Whilst we do not suggest that the record of, and deductions 

 drawn from, this investigation are exceptional, we may say that 

 in our opinion mere estimations of numbers of bacteria in milk 

 appear to us to be scarcely worth the labour involved. What is 

 required is a careful, prolonged, and systematic study of the 

 behaviour of bacteria in milk. In relation to this matter of numbers 

 of bacteria there are, however, two points which require to be 

 briefly mentioned, and it may be convenient to do so here. 



First, the enormously high figures reached in the above records 

 may seem at first sight to be almost impossible. In considering this 

 subject, it is important to remember the extremely rapid multiplica- 

 tion which occurs amongst bacteria, particularly in a favourable 

 medium. This differs somewhat widely in different species. The 



' See also Journal of Experimental Medicine^ vol. v., 1901, p. 313. (E. O. 



Jordan.) 



