112 The Lungs, Heart, and Blood-vessels of the Slug. 



are of two sorts j* one opaque and granular, the other clear 

 and possessed of a nucleus. The corpuscles may be obtained for 

 examination by pricking the sinus of the heart and placing a drop 

 of the fluid, which exudes, upon a glass slide. If now we remove 

 this and examine it with a power of four hundred diameters, 

 we shall see the two varieties. It is possible that at first we 

 may see only the opaque forms, but by treating them with 

 water we render them transparent, and their nuclear and 

 other contents quite perceptible, as shown in the plate, 

 fig. 3. It is strange that although colourless blood is the 

 rule among the gastropoda, the planorbis has a circulating fluid 

 of a reddish hue. 



The peculiar glandular apparatus which surrounds the 

 heart, and which I have called the pericardial gland, has been 

 called the kidney by anatomists, and writers upon this subject. 

 It is exceedingly wrong to style an organ a kidney merely 

 upon a vague supposition that its function may be that of an 

 urine gland, when its structure and position do not seem to 

 support such a view. Yet this is what has been done by 

 Cuvier, Jacobson, Miiller, Siebold, and a host of others. Let 

 us see what grounds there are to support this opinion. 



In the urine of most animals is found a peculiar insoluble 

 substance termed uric acid. Now, chemists have discovered 

 that where this is acted on by aquafortis (nitric acid) and harts- 

 horn (ammonia) a characteristic red colour is produced, and 

 since there is not any other substance (?) capable of being 

 affected in a similar manner, it follows, logically enough, that 

 if in this organ of the slug we find a material whose chemical 

 reaction with aquafortis and hartshorn is similar to that of uric 

 acid, that material must be uric acid. Jacobsonf asserts most 

 positively that he has found a deposit in the heart gland of the 

 slug which gave rise to a reddish stain when acted on by aqua- 

 fortis and subjected to the fumes of hartshorn — hence the 

 deduction. 



I have made a series of experiments upon the same subject, 

 and have invariably found — 



1st. That the stain was not of tho ordinary red hue, but of 

 ;i dirty reddish brown. 



2nd. That it was produced by the aquafortis alone without 

 the employment of the hartshorn, and 



3rd. That the sumo stain was produced when portions of 

 the liver had been placed under similar conditions. 



* This was first distinctly indicated by Mr. Wharton Jones in his admirable 

 memoir in the Philosophical Transactiona for 1846; for though Leydig described 

 two forms of corpuscles in bifl admirable memoir, Ueber Paludina Vivipara, yet 

 he was ignorant of their developmental relations to each other. 



| Meckel's Archives, V I., p. :570. 1820. 



