XII 



AUTHOR'S PREFACE. 



in tantam laminam extendatur, nondum satis mihi constat : 

 certe principio increscere volumen cellulse, nescio an imbibitione, 

 constabit, nisi spes fallit, promotis disquisitionibus." The 

 cantion with which Henle (and, indeed, every good physiolo- 

 gist) expresses himself in this passage with reference to the 

 true growth of non-vascular tissues, is the best illustration of 

 the state of the question. There is another observation of 

 Henle's, which is opposed to the epithelium being regarded as 

 a lifeless substance secreted from the organised tissue; I allude 

 to the passage (1. c. p. 22 et seq.) where he proves that the 

 vibratile cilia, whose motion it is so difficult to explain by 

 physical laws, stand upon little cylinders which are merely a 

 modification of the epithelium. 



Turpin (Annal. des Sciences natur. vii, p. 207) showed that 

 the corpuscles, which Donne had found in vaginal discharges, 

 and regarded as cast-off epithelium, were organised cells, and 

 were in general oblong, and either pointed at one or both 

 ends, or. altogether irregular in figure, and that a new gene- 

 ration of spherical vesicles 1 took place in their interior. He 

 then remarks (1. c. p. 210) : " On ne peut s'empecher, apres 

 avoir bien etudie les vesicules dont est formee la couche de 

 mucus produite par la membrane muqueuse vaginale, d'y voir 

 un tissu cellulaire bien organise et compose comme tous les 

 tissus cellulaires vegetaux, d'un agglomerat, par simple conti- 

 guite, de vesicules distinctes et vivant individuellement chacune 

 pour leur propre compte au depens de Feau muqueuse, qui les 

 baigne de toutes parts." Turpin then compares this tissue of 

 animal cells, presented under the appearance of mucus, with 

 what he calls " suppurations vegetales, excretions muqueuses, 

 qui semblent suinter sous forme de gouttelettes, de la surface 

 des tissus vifs," and which is generally comprised under the 



1 May there not have been some confusion here with the nuclei of the epithelium- 

 cells ? At present, as far as regards Mammalia at least, we know of no formation 

 of cells within cells in the epithelium. 



