140 
IOWA ACADEMY OE SCIENCES. 
These observations led to the constant use of lactose media 
when it was desired to make a quantitative estimate or to 
isolate the acid organism. 
A more recent study of the work done by various inves- 
tigators led to the conclusion that much of the counting of 
bacteria which has been done is of little value on account 
of the kind of media used, and the lack of knowledge 
regarding the relation it bears to the number of organisms 
developed. It is also evident that mistakes, due to the 
same cause, have been made in regard to the kind of 
bacteria most common in milk. The most common mis- 
take has been a failure to recognize that the bacterial flora 
of milk is composed, as largely as it is, of acid- producing 
bacteria, mostly of a single species. In order to get a 
definite result a short series of experiments was recently 
undertaken with the following objects in view: 
First — a. To find how the number of milk bacteria 
developing on peptone agar compared with number grow- 
ing on the same media with 2 per cent lactose added, b. 
Same comparison between ordinary peptone gelatin and 2 
per cent lactose gelatin, c. Same comparison between 
peptone and lactose gelatin and peptone and lactose agar. 
Second . — What effect does the kind of media have on the 
relative proportion developing, of those causing acid coag- 
ulation; those having no effect on milk; and those coag- 
ulating by action of an enzyme? 
