REPORT ON ANIMAL PHYSIOLOGY. 129 



destroys life by mechanical interruption of the circulation. For 

 small quantities even of irrespirable gases (except nitrous, sul- 

 phuretted-hydrogen, and ammoniacal gases,) are not fatal. 



The interesting and difficult inquiry into the causes which 

 produce coagulation of the blood has lately been ably resumed 

 by Mr. Prater. His numerous comparative experiments show 

 how important an element is the quantity of the agent which 

 modifies that process : that the same agent which in a large 

 quantity altogether prevents coagulation, in a small quantity 

 favours it. He confirms also the fact, announced by Schroeder 

 Van der Kolk, that as the proportion of serum is relatively in- 

 creased, (as it is in blood last drawn,) so is the tendency to coagu- 

 lation also increased. The impression derived from his works 

 is one which strengthens our belief generally in the views of 

 Hunter ; viz. that no theory can satisfactorily explain the phee- 

 nomena of coagulation which has not a regard to the vital pro- 

 perties of the blood ; properties whose variations v/e are not yet 

 able to connect with those cori'esponding alterations in the com- 

 position and aggregation of its molecules which we cannot but 

 believe to accompany them, Mr. Prater attempts to infer from 

 his experiments what the vital properties of the blood are which 

 have hitherto been ascertained; viz. vital elasticity (irritability), 

 and contractility. See Essay on the Blood, and Experimental 

 Inquiries in Chemical Philosophy . 



The Powers ivhich circulate the Blood. — From the observa- 

 tions of Prevost and Dumas, of Baer, and of Baumgsertner, we 

 find that many important organs of the body are traced out in 

 the primitive matter of the germ, before there is any indication 

 of blood or of vessel to contain it. According to Baumgaertner*, 

 the motion of the blood is first perceptible in the Frog and Sala- 

 mander seven or eight days after the rudiments of the brain and 

 cord are visible, and even twenty- five days after that time in the 

 Trout. In the same way rudimentary shapes, corresponding to 

 skin and organs of sense, muscle and bone, digestive and respi- 

 ratory organs, are traced out in the original organic matter be- 

 fore they receive any blood. The vessels and the blood which 

 make up the first circulation between the vascular area and the 

 heart, are formed simultaneovisly from the granular mass which 

 has accumulated between the serous and mucous laminae of the 

 germinal membrane. The granules, gathering together into iso- 

 lated masses, present fissures between them containing a yellow- 

 ish fluid which gradually becomes red. The fissures increase in 

 number; the masses diminish in individual magnitude, whilst 

 they extend the vascular area over a larger space. In these 

 * Beohacldungen iiber das Bhit und die Nerven, quoted by Burdacli. 



1834. K 



