A Criticism of the Cell-Theory; being an Answer to Mr. Sedgwick's ...

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160 GILBERT 0. BOURNE. by those who use it to tighten the bonds of the cell-theory is. to loosen them altogether, and to hand us over unbound to Mr. Sedgwick, who would fetter us once more with a new doctrine, viz. there is no cell, all organisation is a specialisation of tracts and vacuoles in a continuous mass of vacuolated protoplasm. We do not want to be bound, at least I do not, and if we are to be free we must take refuge in some such lax but comprehensive statement as that of von Sachs, viz. that cell formation is a phenomenon very general in organic life ; but even if we must regard it as only of secondary significance, it is the characteristic expression of the formative forces which reside in organic substance. Now this statement affirms the existence of cells, and it is necessary to arrive at some understanding as to what is a cell; what properties are connoted by this term ? It has become abundantly evident in the course of this argument, that whatever other attributes may be affirmed of the cell, the possession of a nucleus is one of the most important. It is impossible to disagree with Pfitzner when he writes, "Wenn wir aber den Kern iiberall und zwar immer und in alien Stadien als durchaus selbstiindiges Gebilde finden, so ergiebt sich deraus dass er fur das Bestehen der Zelle als solchen ein Organ von wiel fundamentaler Bedeutung ist als wir bisher geneigt werden anzunehmen." This is also the view of 0. Hertwig, and it is no new one, for Max Schulze insisted upon it, and Hackel wrote in 1866, "Ein Plasmaklumpen ohne Kern ist keine Zelle mehr." But can we follow Pfitzner when he goes further and says, " bei einer so ausserordentlich Konstanz in der ganze Reihe der Thierformeu, von den Protozoen bis zu dem Menschen, kann ich nicht umhin auzunehmen dass iiberhaupt die ganze Existenz eine Zelle als biologische Einheit an das Vorhandsein eines centralen Korpers, von komplicirten inneren Bau, gebunden ist, dass also die Chromatinstrukturen nicht etwas sekundaren erworbenes, sondern die Grrundbediugung vitaler Existenz der Zelle darstellen. Uud weiter folge ich hieraus
A CRITICISM OF THE CELL-THEORY. 161 das der als Karyokinese bezeichnete Vorgang nicht ein specielle Kerntheilungsmodus, sondern der Kerntheilungsmodus tear' E^o^/jv ist " ? I think not. Particles of chromatin scattered through the protoplasm do not constitute a nucleus any more than a heap of bricks constitutes a house. Under such a view, Ciliata like Trachelocerca phsenicopterus and Chaenia teres would not be cells, for they have no central nucleus of complex structure, nor have Oscillaria and Bacterium, in which chromatin granules have been discovered. Though the case of Holosticha scutellum, in which scattered nuclei (chromatin particles) unite and fuse to form a single central body or nucleus previous to division, may help to clear our ideas, it is evident that the demand for a central organised constituent is more than the cell conception can bear, especially if the demand carries with it a further demand for the universality of mitotic division in nuclei. In short, before we could accept Hertwig's definition of a cell, we should have to ask and answer the question, What is a nucleus? Here I may stop to ask whether it is worth while to discuss the grounds of a definition which, when made, could not be acceptable to the mind of everyone. An argument about definitions would soon land one in the regions of scholasticism, and I have no desire to enter into subtleties which would tax the powers of a Duns Scotus. To give an answer which shall be beyond all cavil to the question, What is a nucleus ? would be about as easy as to answer how many angels can dance on the point of a needle. The truth is that it is the attempt to frame short concise definitions, applicable without exception to whole classes of phenomena, which leads to trouble. The concepts of biology may and should correspond with the phenomena we observe, but they can very seldom be made into universal propositions. There is no place in the science for definitions as exact and universal as those of geometry. The qualities of a nucleus are not to be defined like those of a point or a line. Such propo- VOL. 38, PART 1. NEW SERIES. L
Page 1 and 2: A OEITIOISM OF THE GULL-THEORY. 137
Page 3 and 4: A CRITICISM OP THE DELL-THEORY. 139
Page 5 and 6: A CRITICISM OP THE OELL-THEOKY. . 1
Page 7 and 8: A CRITICISM OF THE CELL-THEORY. 143
Page 11 and 12: A CRITICISM OP THE CELL-THEORT. 147
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Page 23: A CRITICISM OP THE CELL-THEORY. 159
Page 31 and 32: A CRITICISM OF THE OELL-THEORT. 167
Page 35 and 36: A ORTTIOISM OP THE OELL-THEORY. 171

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