i8o POPULAR SCIENCE MONTHLY. 



of the structure of fishes ; frogs' eggs, tadpoles, and frogs have 

 been almost universally used, while birds and mammals have 

 been largely studied through our investigation of the fowl, the 

 pigeon, and the rabbit. Of course, hundreds upon hundreds of 

 other plant and animal organizations have been most exhaust- 

 ively worked out, but students always, or very frequently, date 

 back to the manuals upon the biology of these old standbys. 

 Gray's Human Anatomy is a very good example of one of these 

 aids to the study of a single vertebrate species — a monograph, as 

 it were. Some day, Mivart's Cat will hold a similar place as a 

 work of reference. I have already referred above to the use of 

 the frog as an animal whereby the biological student may gain 

 much information ; indeed, I do not believe there is a single ani- 

 mal anywhere that, for this or other purposes, has come into more 

 general use. If a common frog be fully studied in all its phases, 

 and a comparative study be made of its entire structure, together 

 with its physiology and habits, the student has made a long stride 

 toward the comprehension of life processes in general, and will 

 find himself landed far within the domain of biology, and very 

 liberally equipped to investigate almost any problem zoology may 

 have to offer. In addition to this, ever since physiology came to 

 be a science, frogs have been used by the researchers in that de- 

 partment whereby to demonstrate some of the grandest truths 

 that men have brought to light. Especially is this true with re- 

 spect to the study of the muscular and nervous systems. Physi- 

 cists also use them extensively, and the medical expert in experi- 

 menting with, or detecting the presence of, a variety of poisons. 

 The circulation of the blood, and the processes of inflammation as 

 seen under the microscope, are now studied by thousands of stu- 

 dents in the laboratories the world over, and they are nowhere 

 better seen than in the web of a frog's foot. Some of the more 

 obscure actions of the heart have been made clear by the study of 

 the entire circulatory apparatus of this useful batrachian. The 

 action of woorara in destroying the properties of the motor nerves 

 has been demonstrated by Bernard upon frogs ; while Matteucci, 

 by the use of a frog's leg, has shown the contrasted action of the 

 direct and the inverse current. The remarkable experiments of 

 Marshall Hall and of Pflliger, on the reflex action of the spinal 

 cord, where the most delicate animal organization was necessary, 

 were made possible by the use of frogs ; while another experi- 

 menter has worked out through them the physiological action of 

 strychnine. Indeed, some of the most important facts. in physiol- 

 ogy have been, and constantly are to-day being, demonstrated upon 

 frogs ; and the list of such conquests, and the light they shed upon 

 this most useful kind of knowledge, are altogether too long to enter 

 upon here. Much is to be learned by simply studying the action 



