in its Relations to Physiology. 435 



derived simply from experiments. No experiments can ever contradict 

 truths derived from the observation of nature. The great difficulty un- 

 der which we labour in our experiments is the immense sacrifice of time 

 and exertion required to imitate the conditions under which the observ- 

 ed phenomena manifest themselves in nature. 



With a knowledge of those conditions our labour is concluded. The 

 safest and most direct way is invariably to study nature for a know- 

 ledge of those conditions, and when we have ascertained them, further 

 experiments serve only to guard us against mistakes, and to suggest 

 useful applications of our knowledge. 



Let us not render our labours futile by creating imaginary difficul- 

 ties ; those which exist already are quite enough for us to encounter. 



Does the pathologist imagine that the chemist is desirous of seizing 

 upon his territory ? Has he acquired a possession in it from whence he 

 may be ejected? Js he anxious to leave the Augean stable uncleansed ? 



It has been discovered that benzoic acid becomes hippuric acid in the 

 animal organism, that the elements of benzoic acid perform a part in 

 the secretory process of the kidneys, that they take a definite and 

 traceable share in a vital operation, and may be employed for a definite 

 purpose. Benzoic acid is a non-nitrogenous compound which can only 

 be produced in the living organism of plants. 



Now, if we find further that animals which, to their aliments, par- 

 take of no benzoic acid, but of other non-nitrogenous substances, 

 likewise secrete hippuric acid in their urine to a considerable amount, 

 whilst the urine of carnivorous animals contains no hippuric acid, am 

 I in error in concluding that other non-nitrogenous substances, differing 

 from benzoic acid, may also be used for the production of hippuric acid, 

 and that they likewise participate in the secretory processes ? 



Now, in hippuric acid J still find the elements of benzoic acid ; and I 

 can by simply adding to benzoic acid another substance produced by the 

 organism, form hippuric acid, whilst, with other non-nitrogenous substances, 

 this is possible only after they have undergone a series of transformations. 

 Does not this fact render it extremely probable, not to say certain, that 

 Vegetable medicinal substances, — themselves the products of the vital 

 force, — may, in a manner exactly analogous, remove abnormal states 

 of the animal body, if, by their composition, they are adapted for 

 undertaking in the vital processes that part which the aliments can no 

 longer perform because some part of the mechanism refuses its co-opera- 

 tion which is requisite to render these aliments fit for this purpose ! 



A lofty pillar may be saved from falling by a very small fragment of 

 stone ; the tooth of a wheel which has become loose in the works of a 



