DETECTION OF TAINTS 193 
of this time a mass of curd will be found at the bottom 
of the can in which there has been a vigorous develop- 
ment of bacteria throughout the test. 
If the sample of milk is free from taint, this curd when 
cut with a knife will he perfectly smooth and close. If, 
on the other hand, the sample contains gas germs, these 
in course of eight hours’ development will have produced 
enough gas to give the curd an open spongy appearance 
when cut. The openings are usually small and round, 
hence the name “pin holes” has been applied to them in- 
dicating holes the size of a pin’s head. 
Whenever, therefore, milk produces a curd that an- 
swers this description it may be taken for granted that it 
contains undesirable bacteria. 
Sometimes the milk may be tainted and vet produce a 
close textured curd, but in such cases the taint can be 
detected by carefully smelling of the curd. 
Precautions. In making a test as above outlined two 
things must constantly be kept in mind: first, that to se- 
cure the desired bacterial development, the temperature of 
the samples must be maintained as nearly as possible at 
98° F., which is accomplished by surrounding them with 
water at a temperature of 103° ; second, that to avoid con- 
taminating one sample with another, the knife used for 
mixing the rennet with the milk and cutting the curd 
‘must be sterilized for each can. The thermometer used 
must also be sterile. 
The temperature of the samples can easily be main- 
tained by using a well insulated box like that shown in 
Fig. 51. When a common tin box is used it becomes 
necessary to change the water in it about once every half 
hour. 
