PHYSIOLOOICAL ACTION OF ORGANIC CHEMICAL COMPOUNDS. 157 



rentier it practically free from sulphocyauato. The crystals from alcohol are 

 hard, opaque, white prisms : from -water they are long, fibrous, silky needles. 

 Both forms are anhydrous." I present specimens of both varieties. 



" Erom the mother liquors more of the urea may be recovered by the same 

 process. The last mother liquors, containing mainly sulphur urea, but also 

 much sulphocyanide, may be evaporated down, and heated again to 170°, as 

 above, with fresh sulphocyanide of ammonium, to furnish more urea." 



Sulpho-urea is much less soluble in water than ordinary urea, requiring 

 twice its own weight, at 60° F., for solution. It has a saline bitter taste, 

 compared by some to the taste of magnesian sulphate. It differs simply from 

 ordinary urea in that in it sulphur replaces oxygen. 



Urea. Sulpho-urea. 



1 CO'* UU1L/U.U-UL ^4 



In order to determine the difference of action of the two ureas, a series of 

 comparative experiments were carried out. The results may be thus epito- 

 mized : — 



On frogs and rabbits sulpho-urea differs materially from common urea in 

 its action, i. e. when used in the same quantities. The first produces definite 

 convulsive action, with coma and convulsion ; the second produces, in frogs, 

 coma without convulsion, and in rabbits nothing more than a slight and gentle 

 soporific condition, which lasts for a very short time, and can be broken at 

 any moment by the simple act of moving or calling out to the animal. 



In frogs sulpho-urea induces the saline cataract, common urea does not. 



To produce any decided physiological effect with sulpho-urea, the proportion 

 used must not be less than thirty grains to the pound weight of the animal. 

 In three experiments in which it was administered to young rabbits, to the 

 extent of producing slight soporific effects, it reduced the animal tempera- 

 ture two degrees Fahrenheit within the interval of an hour. 



The impression I have gathered in respect of sulpho-urea is, that it is a 

 saline narcotic, and as such it may prove of use in medicine ; but the great 

 point of physiological interest in connexion with it lies in the difference 

 indicated, by its means, between the action of oxygen and sulphur in com- 

 bination with the same elements, C, N, H, in the same form. The difference 

 may be due to the difference of weight, or it maybe due to difference of solu- 

 bility ; the elements, oxygen and sulphur, producing the distinction by virtue 

 of their physical qualities of weight or solubility ; or it may be due to the 

 special qualities of the elements. I offer these thoughts as again bearing upon 

 the general question of chemical composition in relation to the physiological 

 action of chemical substances. 



CmOK-ETHTIIDENE MoNOCHLOETTRETTED CnLOEIBE OP ElHYLE. 



In the year 1852 Dr. John Snow introduced as an anaesthetic the mono- 

 chloruretted chloride of ethyle. He administered the vapour of this substance 

 many times to the inferior animals and to the human subject, and he came 

 to the conclusion that the vapour was equivalent in value to chloroform, and 

 had an advantage over chloroform, viz. that it rarely if ever produced vomit- 

 ing ; it did not usually excite the stomach, he observed, even if it were ad- 

 ministered after food. In 1870 the distinguished Liebreich, who evidently 

 was not aware of Snow's research, reintroduced this anaesthetic under tho 

 name of chlor-ethylidene. Chlor-ethylidene yields a sweet etherial vapour, 



