STRUCTURE OF THE GERM. 227 



food passes, and during that passage is so worked up as to 

 yield to the animal those particles fit to be appropriated by 

 the new body, and become a part of it. But a growing germ 

 has no alimentary canal, and yet it grows. In the adult 

 animal, the food thus elaborated is absorbed, passes into the 

 blood-vessels, and is circulated through all parts of the body. 

 This fluid, resulting from the action of the alimentary canal, 

 and circulating in the blood-vessels, is the nourishing fluid 

 upon which the animal is properly fed. By this fluid are 

 produced all those secretions which are elaborated by the 

 body. But the germ has no blood ; it has no vessels, it has 

 no heart ; it has no circulation ; and yet it grows. Nor does 

 the difference stop there. An adult animal which digests, 

 and circulates the nutritive food, breathes; that is, this fluid 

 is submitted to the influence of the atmosphere, exchanges 

 some of its parts, takes in some, gives out others, and, in 

 that way, the whole organism is maintained in a condition fit 

 to keep it alive. But in the germ there is no breathing, 

 there is no organ of breathing, and yet it grows. 

 , We must learn a new physiology before we shall understand 

 the development of the germ. We have here a living being, 

 destitute of organs, yet growing and performing all those 

 functions, which are carried on later through distinct sets of 

 organs. It is something marvellous. It has taken investi- 

 gators half a century to understand that such a thing could 

 be. When I was a student, there were still physiologists 

 who maintained that all the organs necessary for the main- 

 tenance of life existed in miniature in the germ ; that they 

 grew as the germ grew, and performed their functions as they 

 enlarged. They would not give up this idea until they 

 were forced to do so by the demonstration, under the micro- 

 scope, of the condition of the germ in its earliest stages. All 

 then admitted that a particle of yolk, imperceptible to the 

 naked eye, hardly visible with the highest magnifying powers 

 of our best microscopes, was an incipient new living being, 

 capable of maintaining its life, and of passing through a suc- 

 cession of changes, by which in the end, it built its own 

 organs, developed them, so as to enable them to acquire and 

 perform their functions, and finally to manifest life as it is 

 seen in the adult animal. 



