REGULATORY SUBSTANCES 521 



individuals) of Paramoeciiim were greater in the sulphhydryl- 

 containing cultures. The skin of mice was rubbed with the 

 sulphur compound. Histologic examination showed an increase 

 in the growth of the epithelial tissue of the treated animal as 

 compared with the control (Fig. 179). The next step was appli- 

 cation to the human being. Here, again, the sulphur-containing 

 compound (thioglucose) activated cell division, thus producing 

 the healthy growth of new tissue and the healing of wounds. 

 Thiocresol and cysteine proved to be more successful than 

 thioglucose. 



If we briefly summarize the contributions of Hammett, they 

 are that sulphhydryl, R — SH, compounds stimulate growth, 



while partially oxidized sulphinate, R — S\ ' and sulphoxide, 



\0H 



R — S — R, derivatives retard growth. 



11 



O 

 Sulphur is generally regarded as a very important element in 

 the growth of an organism (page 432). Complex substances, 

 such as the body fluids of an embryo, may owe their remarkable 

 growth-stimulating powers to sulphur groups. The advances 

 in the biochemistry of growth-stimulating and regulatory sub- 

 • stances are so great and come so rapidly that no review is ade- 

 quate. The auxin work of Went is now supplemented by that 

 of P. W. Zimmerman who finds that many substances (e.g., 

 carbon monoxide) induce the formation of adventitious roots. 

 Murneek shows the relation between asparagine in plants and 

 urea in animals. Harington has synthesized glutathione; and 

 Ruzicka has added to the list of male hormones. Especially 

 significant are the remarkable accomplishments in the artificial 

 production of hormones and other regulating substances (e.g., 

 ascorbic acid and hormones of the male and corpus luteum). 



