HISTORY AND METHODS OF INVESTIGATION. 13 



vestigator we have become familiar with the peripheral and central nervous 

 systems of representatives of numerous classes of invertebrates. The vital 

 methyl-blue staining, which more than any other has made these results 

 possible, is very perishable, and work with it is difficult, requiring exact 

 estimation of the proper time, etc. So the process recently taught by Bethe 

 for fixing, hardening, and cutting the tissue stained with methyl-blue was 

 welcomed gladly. 



It is to be expected that the method in its present perfection will make 

 possible an especially rapid progress of knowledge. 



The means to the end are many. For every single problem one must 

 always ask the question: What method is to be applied that one will have 

 to meet only the simplest relations? Seldom will the study of the organs 

 of adult man lead to trustworthy results; it will usually be necessary to 

 create artificially greater simplicity. 



Prom time to time it has been attempted to comprise in a schematic 

 drawing what was known of the minute anatomy of the nervous system. 

 The oldest schematic representation of the brain-tracts known to the author 

 is that of Descartes, in "Tractatus de Homine," which appeared in 1663. 

 Among the older representations belonging to this class may be enumerated: 

 schemes of the spinal cord by Kolliker, by Ludwig, by Bidder, and by 

 Leydig, and the renowned schema of Stilling. The diagrams of Meynert, 

 of Aeby, and of Plechsig include a larger field, — from the spinal cord to the 

 Corpora Quadrigemina, — ^while that of Jelgersma includes the entire nerv- 

 ous system. 



In the following chapters the reader will often find in the figures and 

 in the statements what is really only a sort of schema. Such a method serves 

 the purpose of presenting in the clearest possible way the most important 

 facts regarding the nerve-tracts of the central nervous system. Not only 

 are lines drawn to represent facts won by purely anatomical methods, but 

 also to represent those tracts which eovld be determined by well-observed 

 pathological facts. A schema is not always a picture of nerve-tracts; it is 

 often simply a graphic representation of the conclusions which may be 

 drawn from numerous observations. A schema is a tottering structure. It 

 must be repaired, sometimes here, sometimes there: or often in part torn 

 down and reconstructed. It has been contended that one has no right to 

 construct schemata in a field where there are so many deficiencies as in our 

 knowledge of the central nervous system. But let us Join with the venerable 

 Burdach, who wrote in 1819: "It is not alone necessary to collect building 

 material. In every period in which a new mass of material is collected we 

 must start anew to erect an edifice. This giving of definite form to the 

 knowledge will in no way retard the spirit of inquiry which leads to new 

 discoveries; on the contrary, it is only when we get a comprehensive view 



