194 General Consideration of Function [CHAP. 



In the literature to which I have had access evidence of this nature is very scanty, 

 in fact, I can only refer to the previously mentioned naked-eye observation of Zuckerkandl, 

 and to some experimental researches of Lowenthal. Lowenthal in a number of instances 

 divided the olfactory bulb either near its entry to the olfactory lobe, or where it lies 

 over the tip of the frontal lobe, and after examining the brain by the method of Marchi 

 arrived at the following conclusions: (1) The tractus olfactorius lateralis is to be regarded 

 exclusively as a tract of the second order. (2) Fibres of the mesial olfactory tract springing 

 from cells of the anterior olfactory lobe pertain to the third and higher order, and they 

 end in the lobus pyriformis and cornu ammonis of both hemispheres, and partly in the 

 bulbus olfactorius of the opposite side. (3) There is a partial decussation of tracts of the 

 higher order. (4) The anterior commissure conveys a number of such fibres. (Probst and 

 Ramon y Cajal have conducted researches of a similar but less comprehensive nature.) 



Although carried out in the lower animals, experimental observations like those of 

 Lb'wenthal's help to elucidate this difficult subject, but at the same time it can hardry be 

 denied that a determination of the distribution of scattered degenerated fibres is less likely 

 to lead to exact information on localisation in this region than an analysis of the reactive 

 degeneration, which will probablj" be found to occur in the cells which serve for the 

 reception or interpretation of olfactory sensations, when these cells are cut off from the 

 influence of such impulses. 



Reviewing the situation from the histological standpoint, we are driven to confess that 

 while our knowledge of the normal histology of the olfactory apparatus and of the parts which 

 probably govern this function is very complete, more pathological evidence of a definite and 

 confirmatory character would be gladly welcomed. 



The Localisation of the Sense of Taste. 



The sense of taste differs from that of smell in that the nerves concerned in its 

 conveyance pertain to the category of cranial nerves, whereas, strictly speaking, those for the 

 conduct of olfactory stimuli do not. With the auditory nerves, however, the nerves of taste are 

 analogous, but while our knowledge of the central course and connections of the auditory 

 nerves is almost complete, it is quite the reverse with those of taste. True it is that we 

 have abundant evidence to the effect that peripheral severance of the glossopharyngeal 

 nerve, and of the trigeminal nerve after it has been joined by the chorda tympani, is 

 followed bj- loss of the sense of taste in certain divisions of the tongue, but as to the 

 cerebral connections and destinations of these nerves we are almost completely in the 

 dark. 



It is assumed that the cortical centre for taste is located in the lobus hippocampi in 

 the neighbourhood of the olfactory centre, but the grounds for this assumption are hypo- 

 thetical, and no clinical or experimental observations sufficiently precise to prove it have 

 been recorded ; in fact, Gorschkow on experimental and Bechterew on clinical grounds have 

 deserted the hippocampus and locate this function in some part of the operculum. In dis- 

 cussing the Insula I shall return to the findings of these observers. 



