xii AUTHOR’S PREFACE. 
in tantam laminam extendatur, nondum satis mihi constat : 
certe principio increscere volumen cellulze, nescio an imbibitione, 
constabit, nisi spes fallit, promotis disquisitionibus.” The 
caution 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. vu, p. 207) showed that 
the corpuscles, which Donné 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’ took place in their interior. He 
then remarks (1. c. p. 210): ‘On ne peut s’empécher, aprés 
avoir bien étudié les vésicules dont est formée la couche de 
mucus produite par la membrane muqueuse vaginale, d’y voir 
un tissu cellulaire bien organisé et composé comme tous les 
tissus cellulaires végétaux, d’un agglomérat, par simple conti- 
guité, de vésicules distinctes et vivant individuellement chacune 
pour leur propre compte au dépens de eau 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 végétales, excrétions muqueuses, 
qui semblent suinter sous forme de gouttelettes, de la surface 
des tissus vifs,’ and which is generally comprised under the ~ 
' 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. 
