26 RESPIRATION. TEMPERATURE. 



of all the posterior half of the body only receive imperfectly 

 arterialised blood. Until lately, it was believed that, in other 

 animals of this class, (the Batrachians,) there was, on the con- 

 trary, but a single ventricle, but it has been demonstrated to be 

 otherwise. 



20. Respiration is carried on with little activity in reptiles ; 

 most of these animals consume but little oxygen, and can be 

 deprived of it for a long time without becoming asphyxiate. 

 Temperature exerts the greatest influence over this function, and 

 in the warm season, the necessity of breathing is more vividly 

 felt than in winter. A frog, for example, deprived of air in the 

 summer, perishes in less than two hours; while in winter, it will 

 continue to live for several days. In some reptiles, there are 

 branchiae (gills,) during the early period of life; but the lungs are 

 soon developed, and then the branchiae disappear, so that the same 

 animal has at first an aquatic, and afterwards an aerial respira- 

 tion : there are some even that preserve these organs throughout 

 life, and which, having lungs at the same time, are completely 

 amphibious; but most reptiles have lungs only. We must not 

 conclude however, that their respiration is exclusively aerial ; 

 for, in many of these animals, the skin is also a respiratory organ, 

 and can act on the air dissolved in the water as well as upon the 

 oxygen of the atmosphere. In some reptiles, this cutaneous res- 

 piration is even so active as to be, under certain circumstances, 

 sufficient for the maintenance of life. 



21. The organization of the lungs is not favourable to great 

 activity of respiration ; their air cells are very large, and conse- 

 quently the vascular surface designed for contact with the air, 

 is but of little extent. They are not lodged in a peculiar cavity, 

 the thorax not being separated from the abdomen by a diaphragm, 

 and the air is renewed in them with less facility and less regu- 

 larity than in the superior animals. 



22. Reptiles are all cold blooded animals, that is, they do not 

 produce sufficient heat to maintain a temperature above that of 

 the atmosphere. Their whole body is warmed or cooled at the 

 same time with the surrounding medium, and the changes of 

 temperature which they experience powerfully influences all their 

 functions A temperature of about one hundred, to one hundred 

 and twenty degrees of Farenheit's thermometer, is promptly fatal 



20. What is the character of respiration in reptiles ? How is it influenced 

 by different temperatures 'f Is it always carried on by the means of lungs, 

 "21. How do the lungs differ in organization and situation from the same 

 organs in mammals? 



22. Why are reptiles called cold blooded animals ? What are the effect* 

 of temperature on the vital phenomena of reptiles ? 



