728 THE PHYSIOLOGY OF REPRODUCTION 



nervous system usually die very rapidly. The same is true of 

 the gland-cells ; but the muscles may remain sensitive to external 

 influences for many hours. In animals it has been shown that the 

 heart itself after removal from the body, if kept under suitable 

 conditions and perfused with an artificial fluid resembling blood-serum, 

 may continue to live and undergo rhythmical contractions for a 

 considerable time. In the process of death-stiffening, or rigor mortis, 

 the muscles once more contract spontaneously, and not till this has 

 happened is their life utterly extinguished. Rigor mortis is brought 

 about by the coagulation of the muscle plasma within the cells. It 

 begins at periods varying from half an hour to thirty hours after 

 somatic death, and it continues for an average of about thirty hours. 

 Certain cells may even live for some time after rigor moi'tis has passed. 

 This is notably the case with the ciliated epithelial cells of the inner 

 surface of the respiratory passages, and with the white corpuscles of 

 the blood. Sooner or later, however, every part of the organism 

 perishes, putrefactive changes set in, and the entire substance of the 

 body passes once more to 'that " dust " out of which its vital activities 

 enabled it to build itself up in the progress of individual life. 



