366 
ALFRED L. LOOMIS. 
be again found in the diseased body—we have no alternative—we 
must conclude that we have ascertained the cause of the disease. 
The importance of being familiar with the etiology of disease 
before we can expect to combat it with any well-grounded hope 
of success is evident. 
The three steps I have alluded to are surrounded with diffi¬ 
culties, and if you will follow me I will endeavor to indicate some 
of them. 
Let us suppose, for example, that we wish to repeat the work 
of Koch with the bacillus of tubercle. Let me premise by saying 
that it is believed that certain little rod-like forms are invariably 
found associated with tubercle. If the sputum of a phthisical 
patient be submitted to the skilled mieroscopist he is always able 
to demonstrate the bacilli. This goes for very little. Because 
bacilli are found in phthisis it is no more certain that they are 
the cause of phthisis than is it certain that cheese-mites are the 
cause of cheese. But if with these bacilli we can inoculate a per¬ 
son, and thus produce tuberculosis, we have the chain complete. 
Well, supposing we were to inject some sputum from a phthis¬ 
ical person into the blood of a healthy person, and then boldly 
announce to the world that you have demonstrated the relation 
of cause and effect between the bacilli and phthisis. You would 
start such an uproar of objection as would speedily convince you 
that there was much work yet for you in the domain of bac¬ 
teriology. 
Among these objections would appear this, and very properly 
too : “ You have injected in the blood of your unfortunate patient 
pus, morphological elements, and, perhaps, half a dozen other 
forms of bacteria with the sputum, any one of which are just as 
likely to prodnce the lesion as the bacillus you have selected.” 
So you must begin again. You must first isolate your 
bacillus. 
It is a fortunate fact in the biology of bacteria that nearly 
every specimen has a peculiar mode of growth. If I were to take 
a glass plate, one side of which is coated with a thick solution of 
hot, peptonized gelatine, and allow the latter to cool, the gela¬ 
tinous matter will become solid. If, now, with a wire dipped in 
