ETIOLOGY. 27 



the biological sciences. The study of form naturally and necessarily 

 precedes the study of function. The ornithologist finds a new species 

 of bird ; he first studies its shape and size, the color of its plumage, 

 the form of its beak, the number and arrangement of the feathers of 

 the tail and wing, the color of the eyes, etc. All this can be done 

 with a single specimen, recognizing the fact, however, that variations 

 more or less marked are likely to be found in other individuals. 

 More time and wider opportunities for observation will be needed 

 before he can tell where and when this bird is accustomed to build 

 its nest, upon what insects, grains and berries it feeds, with what 

 other species of birds it lives in peace, and with what it is at war, 

 A much greater range of observation and study is necessary before 

 the naturalist can tell how his newly discovered species would thrive 

 if carried to a new climate where it would be compelled to live upon 

 unaccustomed food, to build its nest of strange material, and to 

 encounter new foes. 



We repeat that it is no discredit to the science nor to those who 

 have developed it to say that the study of bacteriology has largely 

 been morphological. Without the morphologist, the physiologist 

 and the physiological chemist could not exist. The science having 

 had for its support largely morphological studies, the deductions 

 and formulated statements arrived at by its students have been 

 reached in accordance with the knowledge obtained from this 

 source ; but since it has been admitted that the causal relationship 

 between a given germ and a certain disease is dependent upon the 

 chemical products of the growth of the germ, the fundamental lines 

 of work must be made to correspond with this knowledge. 



We may briefly enumerate some of the problems that now lie be- 

 fore us in our attempts to study the chemical factors in the causation 

 of the bacterial diseases. In the first place, it will be desirable to 

 define and classify the chemical products of bacterial activity. In 

 doing this it will be desirable at all times to distinguish between 

 those substances which have their origin in the cleavage action 

 of bacteria and those which are formed by synthetical processes 

 within the cell ; but our knowledge upon this subject is not as yet 

 sufficiently advanced, nor does it possess that degree of accuracy 

 necessary before we can determine positively the manner of formation 

 of these substances. In defining and classifying the chemical prod- 

 ucts of bacterial activity we will find quite naturally that there is 

 not complete agreement among those who have worked in this field 

 of science. Every attempt at the classification of bacterial products 

 must at present be regarded as provisional and subject to such alter- 

 ations as future discoveries may indicate. It will also be found 

 that it is not possible in all cases to distinguish between poisonous 

 and harmless bacterial products. This subject will be discussed more 

 in detail later. 



