464 THE POPULAR SCIENCE MONTHLY, 



which the blood is oxidized ; and, within natural orders, it has a rela- 

 tion to the activity of the animal. For example, that of the swallow 

 is 111, hen 109, gull 100 ; among mammals, squirrel 105, cat 101, 

 dog 99, man 98. The animals called cold-blooded are only relatively 

 so, for fishes and reptiles have a temperature somewhat above that of 

 the water or air in which they live. Even the lower creatures are 

 slightly warmer than the surrounding medium. 



The weight of the blood, which is always greater than that of 

 water, depends, of course, upon the amount of solid matter and the 

 abundance of the corpuscles. In man, the red corpuscles constitute 

 one third to a little less than one half the mass of the blood. The 

 blood of birds has the largest proportion ; and it appears that the tem- 

 perature bears a relation to the amount of solid matter. 



The amount of blood is greater in warm-blooded animals ; and the 

 proportio7i of blood to the size of the body increases with the size. 

 The blood of man is by weight about one thirteenth the weight of the 

 body. The dog has blood equal to one fifteenth its body-weight ; 

 rabbit, one eighteenth ; cat, one twenty-first. The amount of blood in 

 the elephant and the whale has not been determined ; but the heart of 

 the whale is three feet in diameter. 



The operation of transfusing the blood of a living animal into the 

 vessels of another, or of one that is dying, was known in ancient times, 

 and has been practiced at intervals for the last three hundred years. 

 Extravagant hopes concerning it were formerly entertained. It was 

 believed that diseases might be cured, impaired reason restored, old 

 age deferred, and even the dead returned to life. In late years the 

 eminent Brown-Sequard states that a dead dog was by this means 

 restored to life for twelve hours ; but the experiment has never been 

 confirmed, and doubtless the animal was not dead, as supposed. It is 

 also stated that a maniac was restored to reason by the blood of a calf. 



In modern medical science, the transfusion of blood has become a 

 well-recognized operation for cases of exhaustion from simple loss of 

 blood. For this it is frequently practiced, and with success in the 

 majority of cases. For general weakness and disease it has sometimes 

 been used, but has not proved reliable. 



The amount of blood used in transfusion is usually a very few 

 ounces, sometimes only one or two drachms rarely ten or more 

 ounces ; a small quantity is safer. The blood of a different species of 

 animal is considered dangerous when used in large quantity. Venous 

 blood is preferred, and may or may not be defibrinated. 



Pure milk has been successfully used instead of blood ; and even 

 artificial mixtures are employed. Richardson kept a monkey alive for 

 several weeks by a daily injection of an artificial blood. 



The veins of the extremities are generally selected for the opera- 

 tion, they being less likely to admit air, which might be fatal by caus- 

 ing coagulation. 



