222 ZOOLOGICAL PHILOSOPHY 



to the vital movements, when the blood affected flows to the 

 organs. 



The excessive tension of orgasm under certain conditions in some 

 or all of the soft parts of an individual, although not great enough 

 to break up the cohesion of those parts, is known under the name of 

 erethism. When it is very strong it produces inflammation, whereas 

 when the orgasm is extremely reduced, though not to the point of 

 disappearance, it is generally designated by the name of atony. 



The tension which constitutes orgasm may vary within certain 

 limits, without on the one hand destroying the cohesion of the parts, 

 or on the other hand ceasing to exist. This variation renders possible 

 those sudden contractions and distensions which occur when the cause 

 of orgasm is momentarily removed and then restored. This seems to 

 me to be the chief cause of animal irritability. 



The cause which produces orgasm, or that peculiar tension of the 

 supple internal parts of animals, is no doubt an element in what I 

 have called the exciting cause of organic movements. It is to be found 

 principally in caloric, either in that provided by the environment, or 

 in this combined with the caloric that is constantly being produced 

 in the interior of many animals. 



Indeed an expansive caloric is continually emanating from the 

 arterial blood of many animals, and constitutes the principal cause of 

 the orgasm in their supple parts. It is especially in the w^arm-blooded 

 animals that the continual emanation of caloric becomes remarkable. 

 This expansive fluid is constantly being dissipated from the parts which 

 it distends, but it is as constantly being renewed by the emanations 

 always being given off from the animal's arterial blood. 



An expansive fluid, similar to that which we are discussing, is dis- 

 tributed throughout the environment and incessantly provides for the 

 orgasm of living animals, either by completing what was wanting to 

 the internal caloric, or achieving it alone. 



As a matter of fact, the caloric of the environment assists more or 

 less in the orgasm of the most perfect animals and suffices by itself 

 for that of the rest ; it is especially the cause of orgasm in all animals 

 which have no arteries or veins, that is to say, no circulatory system. 

 Hence all organic movement becomes gradually weaker in these animals, 

 according as the temperature of the environment becomes lower ; 

 and if this reduction of temperature continues indefinitely their orgasm 

 is extinguished and they die. We have only to recall the torpidity 

 that overtakes bees, ants, snakes and many other animals when the 

 temperature falls below a certain point, and we shall then be in a 

 position to judge whether my statement has not some foundation. 



The reduction of temperature which causes many animals to become 



