172 INSECT TRANSFORMATIONS. 



soon after it is swallowed, — a process which often 

 terminates in the production of an acid ; and as 

 acids have a tendency to redden vegetable colours, 

 the red blotches are plausibly ascribed to that 

 cause. This conjecture, \vhich originated with 

 Count Dandolo, has been proved to be the fact by 

 Professor Brugnatelli; who made the very unexpect- 

 ed discovery that the red matter contains uric acid 

 combined with ammonia, and consequently that the 

 disorder is similar in its proximate cause to what is 

 called the red gravel [Lilliia renalis /S, Good) in 

 man. This acid, then, from its excess in diseased 

 caterpillars, impedes the process of nutrition, and 

 prevents the animal from acquiring sufficient strength 

 to throw oft' the old skin when the time for this ar- 

 rives. 



It appears, also, from the experiments of Count 

 Dandolo, that though caterpillars can live longer in 

 air deprived of oxygen, or otherwise contaminated, 

 than warm-blooded animals, yet they do not thrive, 

 and are very liable to diseases, when they have not 

 access to fresh air. In other words, the food which 

 has been digested cannot without oxygen be con- 

 verted into the fluid analogous to blood; and in such 

 cases, as we have repeatedly witnessed, instead of 

 being appropriated to nourisliment, it is thrown into 

 the intestines, producing diarrhoea, or scour, as it is 

 termed by the cultivators of the silk-worm. In this 

 case the inner skin never acquires sufficient consist- 

 ence, nor can the old one ever become dry enough to 

 be cast. 



One of the most singular circumstances respecting 

 the moult of caterpillars, is the manner in which the 

 hairs are disposed in the new skin before moulting. 

 These are not, like the feet and other organs, sheath- 

 ed in the hairs of the old skin, but smoothly folded 

 down in separate tufts; and if the old skin be 



