--------------------------------+--------------+-------------- _Material tested_ | _Amount of | _Percentage_ | precipitum_ | --------------------------------+--------------+-------------- Fowl’s egg-albumin (old) | .0159 | 100 Fowl’s " (fresh) | .0140 | 88 Silver Pheasant’s " | .0075 | 47 Pheasant’s " | .0075 | 47 Crane’s " | .0046 | 29 Blackbird’s " | .0046 | 29 Duck’s " | .0037 | 23 Moorhen’s " | .0028 | 18 --------------------------------+--------------+-------------- Thrush, Emu, Greenfinch, and Hedge-sparrow egg-albumins were tested and gave traces of precipita, as also did Tortoise and Turtle sera. The egg-albumins of the Tortoise, Frog, Skate, and two species of Dogfish did not react. Alligator, Frog, Amphiuma, and Dogfish sera also yielded no results.[45] [45] Nuttall, pp. 345 and 346. By improving the quantitative method in various ways, Welsh and Chapman[46] were able to explain why the precipitin reaction with egg-white was not strictly specific but gave also, though quantitatively weaker, results with the egg-white of related birds. They found that by a new method devised by them “it is possible to indicate in an avian egg-white antiserum the presence of a general avian antisubstance (precipitin) together with the specific antisubstance.” [46] Welsh, D. A., and Chapman, H. G., _Jour. Hygiene_, 1910, x., 177. The Bordet reaction was not only useful in indicating the specificity and blood relationship for animals but also among plants. Thus Magnus and Friedenthal[47] were able to demonstrate with Bordet’s method the relationship between yeast (_Saccharomyces cerevisiæ_) and truffle (_Tuber brumale_). [47] Magnus, W., and Friedenthal, H., _Ber. d. deutsch. bot. Gesellsch._, 1906, xxiv., 601. 5. We must not forget, while under the spell of the problem of immunity, that we are interested at the moment in the question of the nature of the specificity of living organisms. It is only logical to conclude that the fossil forms of invertebrate animals and of algæ and bacteria, which Walcott found in the Cambrian and which may be two hundred million years old, must have had the same specificity at that time as they or their close relatives have today; and this raises the question: What is the nature of the substances which are responsible for and transmit this specificity? It is obvious that a definite answer to this question brings us also to the very problem of evolution as well as that of the constitution of living matter.