In two series of experiments made at the end of 1911 and at the beginning of 1912, new techniques were developed with the view of investigating the problem of prolonging indefinitely the life of tissues isolated from the organism. These techniques are far from perfect and will doubtless be modified in the future. But they have already permitted the establishment of new facts. Fragments of connective tissue have been kept in vitro in a condition of active life for more than two months. As a few cultures are now eighty-five days old and are growing very actively, it is probable that, if no accident occurs, the life of these cultures will continue for a long time. In some cases the rate of growth of the tissues increased in direct ratio to the age of the culture. Fragments of heart pulsated rhythmically at the beginning of the third month of their life in vitro. These facts show that experiments made with these or with more perfect techniques and followed over long periods of time may lead to the solution of the problem of permanent life of tissues in vitro, and give important information on the characters acquired by tissues liberated from the control of the organism from which they were derived.

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The culture of whole organs (1) in the Lindbergh apparatus (2) has required the development of techniques that vary in some manner according to each organ. The purpose of this article is to describe the procedures used in the perfusion of the thyroid gland, the accidents that may happen during the operation, and the effects of the perfusion upon the gland. Technical The technique consists of several parts: preparation of the gaseous medium, preparation of the .fluid medium, preparation of the Lindbergh perfusion pump, transplantation of the gland into the organ chamber, perfusion, and removal of the gland from the pump.

The culture of whole organs (1) in the Lindbergh apparatus (2) has required the development of techniques that vary in some manner according to each organ. The purpose of this article is to describe the procedures used in the perfusion of the thyroid gland, the accidents that may happen during the operation, and the effects of the perfusion upon the gland. TechnicalThe technique consists of several parts: preparation of the gaseous medium, preparation of the .fluid medium, preparation of the Lindbergh perfusion pump, transplantation of the gland into the organ chamber, perfusion, and removal of the gland from the pump.

A cationic biopolymer, chitosan, is proposed for use in artificial tear formulations. It is endowed with good wetting properties as well as an antibacterial effect that are desirable in cases of dry eye, which is often complicated by secondary infections. Solutions containing 0.5% w/v of a low molecular weight (M(w)) chitosan (160 kDa) were assessed for antibacterial efficacy against E. coli and S. aureus by using the usual broth-dilution technique. The in vitro evaluation showed that concentrations of chitosan as low as 0.0375% still exert a bacteriostatic effect against E. coli. Minimal inhibitory concentration (MIC) values of chitosan were calculated to be as low as 0.375 mg/ml for E. coli and 0.15 mg/ml for S. aureus. Gamma scintigraphic studies demonstrated that chitosan formulations remain on the precorneal surface as long as commonly used commercial artificial tears (Protagent collyrium and Protagent-SE unit-dose) having a 5-fold higher viscosity.