376 THE HUMAN SPECIES 



alters the composition of the tissues, either mechanically, as 

 by external violence, or chemically, as by the presence of 

 noxious vapours or gases in the atmosphere. Injury may be 

 also brought about by extreme changes in temperature, such 

 as chilling or freezing, heating or burning, and by extreme 

 rarefaction of the atmosphere at great heights; this, however, is 

 well borne by certain animals (e.g., the condor), though man 

 and other animals are severely affected by it. Other direct 

 causes of disease, of a specific nature, are parasites and poisons. 



Animals are also susceptible to the indirect causes of disease ; 

 but this is less easily seen in wild animals than in domestic 

 animals, whose constitution, hereditary disposition, age, tempera- 

 ment and sex play an important part. 



The symptoms of the processes of disease in man and 

 animals, do not merely consist in the elevation or depression of 

 the body temperature and the concomitant sensations of heat 

 or cold, but in other elementary anomalies of function, such as 

 pain, or loss of sensation, or spasms and motor paralysis. 



Diseases may, in all cases, end either in complete recovery, 

 in one or more relapses, in chronic illness, or in death ; the last 

 may occur either with or without a struggle ; may be sudden, 

 or in the form of a gradual decline. 



In the last case the symptoms observed in man do not differ 

 from those seen in the higher animals ; psychical activities 

 fail, sensation gradually disappears, the temperature becomes 

 irregularly distributed, and the muscles suffer a general loss of 

 power. 



Man, however, differs from all other animals in one point, 

 and that is in his tendency to suicide. No animal, even when 

 suffering from the most severe and painful disease, ever brings 

 its own life to an end. 



All the cases of apparent suicide in certain animals which 

 are detailed in works on natural history and other publications, 

 can easily be otherwise explained if a little quiet thought is 

 given to the matter. Even the scorpions, which if placed in a 

 ring of burning coals run directly into the flames, behave in 

 their rage like other animals, or even like man they lose 

 their heads and rush on to their own destruction. There is 

 never any clear intention of suicide. 



