230 
Dr. Kidd on the 
and coagulating either by heat or by the addition of alcohol* 
A quantity of this fluid, weighing 1.85 grains, being evapo- 
rated under an exhausted receiver, in which was placed dry 
muriate of lime, left a solid residuum of a bright golden 
yellow colour, which weighed 0.25 grains ; this residuum 
was brittle, and had the general properties of solid albumen. 
The foregoing characters render it highly probably that the 
yellow fluid distributed through the body of the insect, re- 
sembles in its nature the serum of common blood, and there 
can be no doubt, arguing physiologically, that this yellow 
fluid is the blood or nutrient juice of the animal. I wish I 
could as satisfactorily show the means employed by nature 
to distribute this fluid through the system of this and other 
animals of the same class ; for, though I cannot hope to dis- 
cover what more experienced and skilful anatomists have 
sought in vain, a heart, namely, and a system of circulating 
vessels ; yet I cannot subscribe to their opinion, that the 
blood transudes through the the coats of the intestines, where 
of course it must be primarily formed, and thence passes, as 
through the pores of a sponge to every part of the body. 
Both Cuvier and M. Marcel de Serres completed a very^ 
elaborate set of experiments for the purpose of ascertaining 
whether the dorsal vessel of insects sends out any lateral 
branches which might serve the purpose of a circulating 
system, or whether any other distinct circulating system 
exists ; but they have entirely failed in their endeavours ; and 
I feel assured, that where such men have failed, others will 
not succeed ; and yet their consequent supposition that the 
blood is diffused through the general substance of the body, 
appears to me very highly improbable. It accords not with 
