62 ON THE STUDY OF PHYSIOLOGY. 



a focus, SO as to form an inverted picture of the object on 

 the retina, just as well in the dead, as in the living organ, 

 provided their transparency be unimpaired. 



The operation, however, of those natural laws, to which 

 living as well as all other bodies are subject, is constantly 

 modified in the former case, by the vital powers ; and this 

 essential element, in all mathematlco-physiological consi- 

 derations, is, by its very nature, fluctuating and indeternu- 

 nate. Uncertainty in the conditions of a problem, whether 

 In respect to their entire number, or to the quantity of each, 

 is an original sin, for which no subsequent accuracy can 

 atone ; and this character, belonging to all the circumstances 

 of almost every case in the animal economy, not only ef- 

 fectually precludes all useful application of mathematics to 

 physiology, but renders their employment a source of nothing 

 but error and confusion. We can very seldom satisfy our- 

 selves that all the data are before us ; and the precise 

 amomit of each cannot be determined in any instance : nay 

 more, variation and fluctuation are essential characters of all 

 vital processes. The totally inconsistent results, at which 

 dlfi^erent mathematical physiologists have arrived, in treating 

 of the same functions, shew us that very little useful service 

 can be looked for from this quarter. One estimated the 

 force of the heart as equal to 180,000 lbs ; another reduced 

 it to 8 oz. ; and both these conclusions are deduced from 

 reasonings clothed in all the imposing forms of the exact 

 sciences. 



The circulation. In which a central impelling machine 

 drives the blood through an arrangement of tubes, seems 

 naturally to fall under the laws of hydraulics : and the course 

 of the blood in its living channels, no doubt, obeys the same 

 laws that govern the transmission of fluids through inani- 

 mate canals. But if we attempt to submit this intricate pro- 

 cess to calculation, we are stopped at the very outset by dis- 

 covering, that, of its numerous conditions, not one Is ascer- 

 tained with sufficient accuracy for our purpose. It would be 

 necessary to know the amount of nervous influence on tlie 

 heart and blood-vessels, the measure of active and passive 



