VITALIZED BLOOD. 233 



ducts, or ducts -which we call blood-vessels. The chick has 

 now a heart, aud that heart begins to contract, to. heave and 

 fall, so that the fluid within is pressed out and a relation 

 besfiiis between the heart and the channels outside. Throuo^h 

 these channels, which are still open, a certain amount of 3'olk 

 is constantly moving aud falling into the current, and it is 

 this yolk Avhich is transformed into blood. This process 

 goes on so rupicllj' that by the time the parts have reached 

 the phase in which I have described them, the fluid is tinted 

 with reddish blood-corpuscles. These blood-discs are only 

 modified j^olk-cells. They have not the character of perfect 

 blood ; they have not all the characteristics of that blood 

 which we make from our .food, when it passes through the 

 vessels into the respiratory organs, and is there transformed 

 into regular blood-discs. In all this we have nothing, I repeat, 

 but the transformation of yolk, through its own agency, into 

 a variety of substances derived from the yolk itself, and so 

 distributed and diiferentiated as to build up a frame having 

 all the properties of the parent animal from which the yolk 

 is derived. 



Here is something wonderful ! Not onl}^ the simplicity of 

 the process, by which these changes are brought about, 

 attracts our notice, but still more marvellous is the fact that all 

 this goes on from within. There is a principle acting by the 

 aid of the substance which holds it, never deviatins: from its 

 course, and always leading to the reproduction of a being 

 like the parent. How that influence from the parent is trans- 

 mitted, there and then, how and what the nature of that 

 transmission or that impression is, stamping, as it were, 

 the new being so indelibly with the character, with the pecul- 

 iarities of its parents, sometimes even with their idiosyncrasies, 

 with those family features in short, or those features of breed, 

 etc., belonging to the individual, these are matters about which 

 we know nothing whatsoever. These are the questions we must 

 now study, by attempting more refined investigations than 

 those which we have been able to carry on to this day. We 

 must try to seize the moment when these peculiarities are 

 imparted to the new being, in order to know how to influence 

 reproduction at that time ; for unless it be done then, it can 

 never be done. It is by a knowledge of what takes place 



30 



