38 ANALYTIC SECT. VI. 
cable to voluntary contraction; or, in other words, 
voluntary contraction contradicts the hypothesis, 
for it is inconsistent to suppose that debility, or a 
diminution of the vital force, can be the cause of 
voluntary contraction. On this principle, also, 
contraction ought to be strongest after death, 
when the vital action has ceased. 
Lxx. The theory of Hoffman has found few 
followers of much reputation; Cullen, indeed, 
gave it a sort of qualified support, but his strong 
mind was probably fettered by the Havierian 
doctrine of irritability. Although I shall, in 
imitation of my predecessors, for the most part, 
treat the vital force as a simple substance, and 
follow generally the theory of Hoffman, I beg 
leave to offer a few arguments for thinking it a 
compound body. | 
Lxxi. No simple substance can, by itself, gene- 
rate caloric; but wherever there is a develope- 
ment of heat, two or more substances combine 
to produce it. Animal heat is a production of 
vitality, which is probably generated by the 
combination of two sorts of vital force, which 
neutralize each other like positive and negative 
electricity. 
“xx. Berselius has proved, as I conceive, that 
to effect the decomposition of any body, the 
co-operation of positive and negative electricity is 
absolutely necessary. From the impregnation of 
