150 Report >S.A.A. Advancement of Science. 



were stains of fowl's blood. We found them to be caused by mam- 

 malian blood. He was huno-, as circumstantial evidence was verj^ 

 strong against him. If he had said thej- were due to sheep's blood, 

 we would not have been able to contradict him, and he might have 

 been ac(iuitted. Nowadays a competent man can actually say 

 whether he is dealing with human blood or not. He can also deter- 

 mine different kinds of meat, even when mixed and smoked in 

 sausages; he can differentiate between the different kinds of milk; he 

 can also detect adulterations of vegetable substances, e.g., he has now 

 a means, previously wanting, of finding out whether wheat-flour is 

 mixed with broad-bean flour or with mealie-meal, and innumerable 

 other adulterations, which have hitherto bafiied the analytical chemist, 

 can now be detected by the biological method. Specific reactions have 

 even been obtained with blood that had putrefied for tliree months. 

 Thus the substance which yields the reaction must be extremely 

 stable. 



The knowledge of these reactions is so recent, and so little is 

 known of the chemical basis on which they are founded, that it is 

 perhaps not safe to build upon them conclusions of universal applica- 

 tion. Still I could not help being struck with the similarity which 

 these reactions indicate between gradations in the series of manj' 

 well-knoM'n organic bodies and the substances that yield the reactions 

 in series of specific organisms. It seems that the reacting, specific 

 substance of one organism stands in a similar relation to the corres- 

 ponding substance in a closely allied organism as, e.g., methyl and 

 ethyl alcohol, and as we find org^jinisms more and more divergent in 

 morphological characters, so i\\ey recede from one another in their 

 reactions, though still belonging to the same series, which may be a 

 genus or natural order. But every biologist knows that between 

 large groups of animals and plants the want of known connecting 

 links has been most annoying to evolutionists. This applies even to 

 many of our natural orders, e.g., Composit?e, grasses, &c. It may be 

 that this want of connecting links is due to the fact that thej^ are 

 impossible, that the essential specific substances in them are built on 

 a diflerent plan, for which the paraffin and benzol gi-oups may per- 

 haps serve as analogies. If these views are correct in the main, they 

 may also give us an idea how it is that when groups once appear, 

 they have been found in manj- eases to be represented almost at once 

 in past geological ages by a large number of species. In other words, 

 we may say that when once a certain chemical combination represent- 

 ing a species was reached, corresponding combinations of the same 

 series could be fornu^d, and were often formed. 



These considerations would certainly lend great support to De 

 Vries's mutation theor}-, which stipulates that .species have not arisen 

 by the gradual selection and accumulation of the most minute 

 fluctuations of previously existing species, as postulated by the 



